US6337977B1 - Roving voice mail - Google Patents

Abstract

In a telephone system providing a voice mail service, a subscriber's voice mail follows the subscriber as he moves. In, for example, a satellite mobile telephone system, a subscriber may roam over wide areas. As he does so he registers sequentially with different satellite access nodes. These nodes may be on different continents. When the subscriber registers with a new satellite access node, the contents of his previous voice mailbox are transferred to a new voice mail box at the new satellite access node. The subscriber's home location register record and the visitor location register record, at the new node, are updated with the number of the new voice mailbox, so that new voice mail can be routed to the correct mailbox.

Description

FIELD OF THE INVENTION

The present invention relates to method of providing a voice mail service in a mobile telephone network having a plurality of geographically dispersed voice mail storage units associated with respective network switching nodes.

BACKGROUND TO THE INVENTION

The provision of voice mail services is well known in the art of telecommunications. Typically, a voice mail service allows callers to leave a recorded message for a subscriber who is unavailable at the time of the call. The called subscriber can then retrieve the messages at a later time.

A problem arises when voice mail services are provided in telephone systems, for example satellite mobile telephone systems and GSM cellular telephone systems, where a subscriber can roam over a wide area, possibly all over the world. In the case of a satellite mobile telephone system, the subscriber would access the system through different ground stations in different countries or on different continents. In the case of the GSM cellular telephone system and the like, the subscriber roves between services provided by different operators, for instance a UK-based subscriber might take his mobile telephone to Australia and use it with a network there.

In each of the these cases, the subscriber's voice mail must be transferred over long distances each time it is accessed from outside the subscriber's home location. Service providers often use other network's lines for communication over long distances and this ad hoc transfer of voice mail does not promote cost-effective use of such lines. Furthermore, a subscriber who has roamed to another network must enter a long string of digits to access his voice mail in his home network. This has two disadvantages. Firstly, it is difficult for the subscriber to remember the sequence. Secondly, the voice mail service does not have the transparency which roaming is intended to provide.

Known satellite mobile telephone systems include the Inmarsat-M system, the IRIDIUM™ system described in, for example EP-A-0365885, the ICO™ system described in, for example, GB-A-2295296 and the ODYSSEY™ system described in, for example, EP-A-0510789.

SUMMARY OF THE INVENTION

It is an aim of the present invention to overcome the afore-mentioned problems by providing for roving voice mail. In other words, a subscriber's voice mail will follow him around.

According to the present invention, there is provided a method of providing a voice mail service in a mobile telephone network having a plurality of geographically dispersed voice mail storage units associated with respective network switching nodes, the method comprising transmitting the contents of a subscriber's voice mail box in a first voice mail storage unit, associated with a first network switching node, to a voice mail box in a second voice mail storage unit, associated with a second network switching node, said transmission being in response to said subscriber's mobile station registering with the second network switching node, wherein transmittal of the contents of the first voice mail box is effected in reponse to reception, by the first voice mail storage unit, of a voice mail transfer command, the command including a voice mail destination identifier identifying the second voice mail storage unit.

Since, the voice mail is transferred en bloc, a long-distance connection is not required each time a user accesses his voice mail away from his home location. Furthermore, the network control can arrange for the voice mail to be transferred in an economical manner, for instance to ensure that line capacity bought is fully used.

Preferably, the subscriber terminal apparatus is a mobile telephone and the network location of the subscriber terminal apparatus is determined during registration of the subscriber terminal apparatus with the network.

In the case of satellite mobile telephone systems, the user may be on occasion registered with a mobile satellite switching centre other than the one with which he is directly in contact. Accordingly, his voice mail would not be located at the closest node but merely one closer to him than the node which previously stored his voice mail.

Preferably, a method according to the present invention comprises maintaining a database of information relating to a plurality of subscriber mobile stations, the information including the network switching node with which the subscriber's mobile station is registered and a voice mail box identifier; registering the subscriber's mobile station at the second network switching node; updating the database record for said subscriber's mobile station in response to said registration; and transmitting the voice mail transfer command to the first voice mail storage unit. More preferably, the voice mail box identifier stored in the database is altered to identify the second voice mail storage unit when the subscriber's mobile station is subsequently deregistered with second network switching node.

Preferably, the voice mail transfer command is transmitted from the second network switching node.

The present invention finds application in a satellite mobile telephone system, in which case the network switching nodes are preferably comprised in satellite access nodes.

Preferably, a method according to the present invention includes compressing and/or encrypting the voice mail before it is transferred.

Preferably, the timing of the transfer of voice mail is dependent on network traffic level.

The present invention extends to a mobile telephone network including voice mail means operable according to any preceding paragraph of this section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the physical components of a satellite mobile telephone system;

FIG. 2 shows a mobile telephone partially cut away;

FIG. 3 is a schematic diagram of a satellite access node as shown in FIG. 1; and

FIG. 4 is a data flow diagram for the system shown in FIG.1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings.

Referring to FIG. 1, a satellite mobile telephone system comprises a plurality of satellite access nodes (SAN)1a,1b,1cinterconnected by a high capacity digital network2 (hereinafter “the backbone network”), a plurality ofsatellites3a,3b, a plurality of a mobile telephones (UT)4a,4b,gateways5a,5b,5cproviding connections between theSANs1a,1b,1cand other networks6, a network management centre (NMC)7, a satellite control centre (SCC)8 and a tracking, telemetry and control station (TT&C)9. The NMC7, the SCC8 and the TT&C9 are interconnected by a lower capacitydigital network10 which is also connected to thebackbone network2. The other networks6 comprise the public switched telephone network (PSTN), cellular telephone networks and the like.

TheSCC8 and theTT&C9 control the operation of thesatellites3a,3b, for instance setting transmit power levels and transponder input tuning, as directed by theNMC7. Telemetry signals from thesatellites3a,3bare received by theTT&C9 and processed by theSCC8 to ensure that thesatellites3a,3bare functioning correctly. During a telephone call, a UT4a,4bcommunicates with asatellite3a,3bvia a full duplex channel comprising a downlink channel and an uplink channel. The channels comprise TDMA time slots on frequencies allocated on initiation of the call.

Thesatellites3a,3bare in non-geostationary orbits and comprise generally conventional satellites, such as the known Hughes HS601 model, and may include features as disclosed in GB-A-2288913. Eachsatellite3a,3bis arranged to generate an array of beams covering a footprint beneath the satellite, each beam including a number of different frequency channels and time slots, as described in GB-A-2293725.

Thesatellites3a,3bare arranged in a constellation in sufficient numbers and suitable orbits to cover a substantial area of the globe, preferably to give full, continuous global coverage. For example,10 or more satellites may be provided in two mutually orthogonal intermediate circular orbits at an altitude of 10500 km. However, larger numbers of lower satellites may be used, as disclosed in. EP-A-0365885 or other publications relating to the IRIDIUM system.

Referring to FIG. 2, a UT4 is generally similar to the units presently available for GSM networks and comprises a codec, a controller, amicrophone10, aloudspeaker11, abattery12, akeypad13, a radio frequency interface, anantenna14, adisplay15 and subscriber identification module (SIM)smart card16.

The codec comprises a low bit-rate coder, which generates a speech bit stream at 3.6 kbits/s, together with a channel coder, which applies error correction codes to the speech bit stream to produce an encoded bit stream at 4.8 kbits/s. The low bit-rate coder is a linear predictive coder. The channel coder uses Viterbi coding. The codec also comprises complementary decoders.

TheSIM16 includes a processor and a non-volatile memory which stores data identifying the subscriber and data for use in encrypted communication.

Referring to FIG. 3, a SAN1 comprises adish antenna20 mounted for tracking satellites, transmitter andreceiver circuits21 including amplifiers, multiplexers, demultiplexers and codecs, a mobile satellite switching centre (MSSC)22 including acontroller23, a visitor location register database (VLR)24 and a voice mail box unit (VMB)25. TheMSSC22 is coupled for communications signals to thebackbone network2, to a gateway and to the transmitter andreceiver circuits21. Thecontroller23 is coupled for data signals to theVLR24 and the VMB25 and may also send and receive data signals via thebackbone network2.

Thecontroller23 responds to addresses on incoming communications signals, from theantenna20, the gateway and thebackbone network2, by controlling theMSSC22 to output the communications signals on the appropriate paths to their destinations, i.e. theantenna20, the gateway or thebackbone network2.

The VLR24 maintains a record of each of the subscribers registered with the SAN1. The VMB25 provides storage space for voice mail messages for subscribers.

Referring to FIG. 4, adatabase30, called the home location register HLR), contains records relating to each UT4. The record contains the UT's identity (International Mobile Subscriber Identity or IMS), the current status of the UT (whether it is “local” or “global” as will be described in greater detail below), the geographical position of the UT, the home MSSC with which the UT is registered (to enable billing and other data to be collected at a single point), the currently active SAN with which the UT is in communication via a satellite, an individual encyphering key, the address of an associated VMB location, typically in the form of an MSISDN number and call forwarding information.

TheHLR30 may be located in the NMC7 (see FIG. 1) or may be distributed among theSANs1a,1b,1c(see FIG.1).

Referring to FIGS. 1 to4, aUT4amay be registered with one of two distinct statuses; “local” in which theUT4ais permitted to communicate only through one local area or part of the satellite system network, and “global”, which entitles theUT4ato communicate through any part of the satellite mobile telephone system.

TheUT4aperforms an automatic registration process, of the kind well known in the art of cellular terrestrial communications, on each occasion theUT4ais used for an outgoing call, theUT4ais switched on and periodically whilst theUT4ais operating. As is conventional, the registration process takes the form of transmitting of a signal identifying theUT4a(e.g. by transmitting its telephone number on a common hailing or signalling channel). The transmitted signal is picked up by one or more of thesatellites3a,3b. Under normal circumstances, the signal is picked up by a plurality ofsatellites3a,3b, and the received signal strength or time of arrival are transmitted, together with the identity of theUT4aand the identity of thesatellite3a,3breceiving the signal, to theHLR30 via the MSSCs22a,22bof theSANs1a,1bfor which thesatellites3a,3bare in communication.

TheHLR30 calculates, on the basis of the received-signal arrival times, the terrestrial position of theUT4awhich is then stored in the UT's record. The identity of theSAN1a,1b, most suitable for communicating with theUT4ais also stored. This is typically found by comparing the stored position of theUT4awith the positions of each of theSANs1a,1b, and selecting the nearest. However, account may also or instead be taken of the strengths of the signals received via thesatellites3a,3bor of other factors such as network congestion which may result, in borderline cases, in the selection of aSAN1a,1b,1cwhich is not geographically closest to theUT4a. The identity of the allocatedSAN1ais then stored in the UTs record in theHLR3, if the allocated SAN has changed. If the allocatedSAN1ais not that previously allocated, theHLR30 modifies the voice mail box location field of the UTs record to identify a VMB location at the allocatedSAN1a.

Once the HLR record has been updated, it is copied down to theVLR24aof the selectedSAN1aand theVMB25bof theprevious SAN1bis informed that the UT4 has registered with anotherSAN1a. TheVMB25bthen compresses and encrypts the voice mail for theUT4aand sends it to theMSSC22aof the allocatedSAN1a, via theMSSC22b. The message received by theMSSC22aincludes the new VMB location for the voice mail and is transferred to theVMB25a, where it is decrypted, expanded and stored, by theMSSC22a.

The HLR voice mail field (MSISDN code) comprises a country code, a network operator code, a SAN code and a code unique to theUT4a. When theUT4aregisters at anew SAN1a, only the SAN code of the voice mail field changes.

Thus, whenever a subscriber registers at anew SAN1a,1b,1c, his voice mail is automatically transferred to theSAN1a,1b,1cwith which he is registered. When a subscriber wishes to access his voice mail, theMSSC22aneed not retrieve the voice mail from anotherSAN1a,1b,1cbut need only retrieve the mail from the local VMB location identified by the subscriber's UT's record in theVLR24a.

Another embodiment of the present invention will now be described, again with reference to FIGS. 1 to4.

When aUT4aregisters, its HLR record is updated as described above save that the voice mail field is not changed. Once the HLR record has been updated, it is copied down to theVLR24aof the selectedSAN1a. TheMSSC22anotes that the voice mail MSISDN indicates theprevious SAN1band generates a new voice mail address identifying a location in theVMB25a. TheVMB25bof theprevious SAN1bis informed that the UT4 has registered with anotherSAN1aand is commanded by thenew MSSC22ato send the contents of the old voice mailbox to thenew MSSC22a. TheVMB25bthen compresses and encrypts the voice mail for theUT4aand sends it to theMSSC22aof the allocatedSAN1a, via theMSSC22b. The stored voice mail messages received by theMSSC22aare transferred to theVMB25a, where it is decrypted, expanded and stored, in the new voice mail location.

When theUT4aderegisters from the network, thecurrent MSSC22asignals the MSISDN for the current voice mail location to theHLR30 which then updates the voice mail field of the subscriber's HLR record.

A further embodiment of the present invention will now be described, again with reference to FIGS. 1 to4.

When aUT4aregisters, its HLR record is updated as first described above save that the voice mail field is not changed. Once the HLR record has been updated, it is copied down to theVLR24aof the selectedSAN1a. TheMSSC22anotes that the voice mail MSISDN indicates theprevious SAN1band generates a new voice mail address identifying a location in theVMB25a. At this point, theVLR24astores both the new and the old voice mail addresses. Accordingly, if the user wishes to access his voice mail, theMSSC22awill attempt to retrieve messages from both theprevious VMB25band thenew VMB25a.

After theVLR24ahas been loaded with the data from theHLR30, theMSSC22ainforms thenew VMB25aof the old voice mail address. Thenew VMB25athen commands theprevious VMB25bto send the contents of the old voice mailbox to thenew MSSC22a. TheVMB25bthen compresses and encrypts the voice mail for theUT4aand sends it to theMSSC22aof the allocatedSAN1a, via theMSSC22b. The stored voice mail messages received by theMSSC22aare transferred to theVMB25a, where it is decrypted, expanded and stored, in the new voice mail location. If the transfer is successful, thenew VMB25binforms theMSSC22awhich then deletes the record of the previous voice mail address from thenew VLR24a.

When theUT4aderegisters from the network, thecurrent MSSC22asignals the MSISDN for the current voice mail location to theHLR30 which then updates the voice mail field of the subscriber's HLR record. If deregistration occurs before the voice mail is transferred successfully, both voice mail addresses are communicated to theHLR30.

Since both voice mail addresses are stored until the voice mail messages have been transferred, theVMB25bmay notify theNMC7 that it has voice mail to transfer and report the amount of data to be transferred and its destination. TheNMC7 then determines when a link to the destination is to be opened, for some other time critical purpose, and signals to theVMB25bthat it should dispatch the voice mail when the link opens.

Two cases of call forwarding to a voice mailbox will now be described.

In a first case, the subscriber is not active or registered in the satellite mobile telephone system. When a call to a UT4 enters the satellite mobile telephone network via agateway5a(see FIG.1), the receivingMSSC22arequests the UT's current location from theHLR30. If the UT4 is not active in the network, theHLR30 replies with notification that the UT4 is not active in the network and, if call forwarding unconditional (CFU) is activated for the UT4, CFU information and the MSISDN number (i.e. voice mailbox address) of the UT's mailbox. The call is then routed from theMSSC22ato the called subscriber'scurrent VMB25b.

In a second case, a call originates with a UT4 and arrives at anMSSC22a. TheMSSC22aagain requests the called UT's location. TheHLR30 replies with this information, identifying aspecific MSSC22b. The call is then connected to theMSSC22bidentified by theHLR30. The call control process at thisMSSC22bmay determine that the called UT4 is busy or unreachable due to a poor radio path. The called subscriber may have specified that, in these cases, call forwarding should take place. If call forwarding is to take place, the called UT's mailbox MSISDN number is retrieved from thelocal VLR24band the call is forwarded to that number, which will usually be in thelocal VMB25b.

It will be appreciated that the foregoing embodiment may be modified for use in GSM networks. In such a system, a subscriber's UT may be registered with a UK network which provides a voice mail service. The subscriber may then travel to Australia and register his UT with a network there. When the UT registers with the Australian network, the HLR record will be copied from the UK network to the Australian network, as in the case of the HLR to VLR transfer described above, and the HLR will instruct the UK VMB to send the subscriber's voice mail messages to a VMB in the Australian network.

Since, the subscriber's voice mail has been transferred to the voice mail system of the, in this case, Australian network, the user need only enter the short local voice mail access number, rather than the long number required in known systems.

Claims (9)

What is claimed is:

1. A method of providing a voice mail service in a mobile telephone network having first and second voice mail storage units associated respectively with first and second geographically widely separated network switching nodes, the method comprising:

receiving a voice mail transfer command at said first voice mail storage unit; and

in response to reception of said voice mail transfer command, dispatching the contents of a voice mail box for a subscriber, located in the first voice mail storage unit to a voice mail box in the second voice mail storage unit;

wherein said voice mail transfer command includes a voice mail destination identifier identifying the second voice mail storage unit to the first voice mail storage unit and is indicative of the transfer of registration of a subscriber's mobile station from said first switching node to said second network switching node.

2. A method as inclaim 1, further comprising:

maintaining a database of information relating to a plurality of subscriber mobile stations, the information including the network switching node with which the subscriber's mobile station is registered and a voice mail box identifier;

registering the subscriber's mobile station at the second network switching node;

updating the database record for said subscriber's mobile station in response to said registration; and

transmitting the voice mail transfer command to the first voice mail storage unit.

3. A method as inclaim 2, wherein the voice mail box identifier stored in the database is altered to identify the second voice mail storage unit when the subscriber's mobile station is subsequently deregistered with second network switching node.

4. A method as inclaim 1, wherein the voice mail transfer command is transmitted from the second network switching node.

5. A method as inclaim 1, wherein the network switching nodes are comprised in satellite access nodes of a satellite mobile telephone system.

6. A method as inclaim 1, including compressing the voice mail before it is transferred.

7. A method as inclaim 1, including encrypting the voice mail before it is transferred.

8. A method as inclaim 1, wherein the timing of the transfer of voice mail is dependent on network traffic level.

9. A mobile telephone network including voice mail means operable as inclaim 1.

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